The present invention relates to thermoplastic molding compositions and more particularly to flame-resistant and impact-resistant polycarbonate compositions with increased chemical resistance and to molded articles produced therefrom.
A flame retardant, chemical and impact resistant, thermoplastic molding composition is disclosed. The composition that contains
(A) an aromatic polycarbonate and/or polyester carbonate,
(B) a graft polymer,
(C) an oligophosphate conforming to a specific formula,
(D) an anti-drip agent, and
(E) a polyhydroxy ether is suitable for preparing molded articles.
Mixtures containing polycarbonates, graft copolymers such as ABS as well as copolymers based on styrene are used for many applications, for example in the automobile, electrical and data technology areas, or in the domestic appliances or sports sector. For many areas of application the plastics materials are rendered flame-resistant. In specific applications, in particular in areas in which the plastics materials come into direct contact with chemicals such as solvents, greases, oils, acids or cleaning agents, it is also necessary that these plastics materials exhibit, apart from an outstanding flame resistance behavior, also an excellent stress crack resistance (i.e. a good ESC behavior). This is the case for example with housing parts of office equipment and kitchen appliances, which are often exposed to the effect of greases and oils or solvents containing the latter. The plastics materials used for these purposes have to satisfy certain fire safety regulations. For example, for specific thin-wall applications it is necessary that the housing parts rate xe2x80x9cV0xe2x80x9d in the flame resistance test according to UL94 V with wall thicknesses of less than 1.6 mm.
In order to influence specifically the flame resistance as well as the mechanical and rheological properties of polycarbonate compositions, certain auxiliary substances such as flame-proofing agents, plasticizers or inorganic materials are added to the compositions. The individual auxiliary substances often influence several properties of the material in opposite ways. For example, the improvement in the flowability of a polycarbonate molding composition achieved by adding plasticizers is as a rule offset by a deterioration in the thermal stability, measured for example according to Vicat B. It has therefore proved difficult to produce suitable polycarbonate compositions having a balanced property spectrum.
Flame-resistant polycarbonate/ABS compositions are known from numerous applications. For example, U.S. Pat. Nos. 5,157,065, 5,204,394 and 5,672,645 describe flame-resistant polycarbonate/ABS molding compositions that contain organic phosphorus compounds such as monophosphoric acid esters, oligophosphoric acid esters or mixtures thereof as flame-proofing agents, as well as fluorinated polyolefins as anti-drip agents. The molding compositions described in these specifications achieve a rating of V0 in the UL94 V fire test with a wall thickness of 1.6 mm. For many applications, such as for example certain thin-walled housing parts, this classification is often insufficient. In this case a V0 rating is increasingly required even with wall thicknesses of less than 1.6 mm, combined at the same time with good mechanical and rheological properties as well as excellent chemical resistance.
WO 99/07782 discloses flame-proofed polycarbonate/ABS molding compositions containing an oligomeric phosphoric acid ester compound based on bisphenol A and an extremely finely divided inorganic compound. The described molding compositions are characterized by improved mechanical properties (notch impact strength, stress crack behavior) combined with good thermal stability. The disadvantage of these molding compositions, however, is that they have an insufficient flame resistance for wall thicknesses of less than 1.6 mm, as is required for thin-wall applications.
In EP-A 0 780 438 it is proposed, in order to improve the flame resistance, toughness and flowability of polycarbonate/ABS molding compositions, to add to the latter in addition to a halogen-free phosphorus compound as flame-proofing agent, also a polyhydroxy ether as flame-proofing synergist. Monomeric organophosphoric acid esters or oligomeric organophosphoric acid esters derived from resorcinol and hydroquinone are preferably used as phosphorus compound. The described molding compositions are characterized by an improved flowability and impact strength as well as a low tendency to crack formation under impact stress. From the examples it can be seen that with the produced polycarbonate/ABS molding compositions, although the afterburn times in the UL94 V test with a wall thickness of 1.7 mm are in fact measurably reduced by the addition of the polyhydroxy ether, nevertheless the rating V0 is not achieved with times of more than 50 seconds. A further disadvantage of the described molding compositions is that they have an insufficient resistance to solvents (ESC behavior).
Finally, in U.S. Pat. No. 5,849,827 polycarbonate/ABS molding compositions that have been made flame resistant are described, in which a reduction in the afterburn time is achieved by adding small amounts of an inorganic powder in nano-divided form.
The disadvantage of the flame-resistant polycarbonate/ABS compositions known in the prior art is that they either have too low a flame resistance with thin wall thicknesses, or even if they have been rendered sufficiently flame-resistant they have insufficient mechanical and/or rheological properties such as flowability and/or too low a thermal stability. In particular it has proved extremely difficult to produce sufficiently flame-proofed polycarbonate/ABS compositions that in addition to a good flowability, toughness and thermal stability also exhibit a sufficient resistance to solvents (i.e. a good ESC behavior).
The object of the invention is to provide a flame-proofed polycarbonate composition having a significantly improved ESC behavior combined with good toughness, high thermal stability and good processing behavior. The polycarbonate compositions should achieve a rating of V0 in the UL94 V flame resistance test even with wall thicknesses of less than 1.6 mm. They should be characterized by a good flowability, and when processed by injection molding should not lead to undesirable deposits on the mold due to bleeding of the flame-proofing additive, i.e. so-called xe2x80x9cjuicingxe2x80x9d.